Control of electric arc lamps



Dec. 7, 1937. BURNS 2,101,789

CONTROL OF ELECTRIC ARC LAMPS Filed Sept. 11 1955 INVENTOR ATTORNEY Patented Dec. 7, 1937 UNITED STATES PATENT OFFICE CONTROL OF ELECTRIC ARC LAMPS Laurence Burns, Revere, Mass, assignor to Hygrade Sylvania Corporation, Salem, Mass., a corporation of Massachusetts Application September 11, 1935, Serial No. 40,048

6 Claims.

This invention relates to electric arc lamps and more particularly to arc lamps of the type in which the main luminosity is derived from a luminescent are through an ionizable medium such as gas or vapor.

A principal object is to provide an arrangement for controlling the arc in a gaseous or vapor arc discharge lamp or the like.

Another object is to provide an arc discharge lamp of the high pressure discharge type, with means to control the position of the arc column between a pair of spaced electrodes.

In lamps of the type wherein the source of luminosity is an are through a vapor or gas at relatively high pressure, it is preferable in many cases to operate the lamp in a horizontal or nonvertical position. This is particularly true of those lamps having a tubular elongated envelope with relatively widely spaced electrodes therein.

However when this type of lamp is in operation,

or gas filling. This bowing of the arc column not only afiects the luminous output but also causes unequal heating of the envelope, with the result that the upper side of the lamp envelope is at a much higher temperature than the lower side. In some cases this excessive heating of the upper part of the envelope may cause it to melt thus destroying the lamp. Accordingly it is another object of this invention to provide a tubular lamp of the luminous gas or vapor are type, with means whereby the lamp may be operated in a horizontal or non-vertical position while maintaining the arc column in a predetermined position within the lamp, preferably along the central or longitudinal axis of the envelope.

A feature of the invention relates to an improved form of magnetic control for maintaining the arc column of a high pressure gas or vapor lamp, in a central or axial position withinthe lamp.

Another feature relates to the means for controlling the position of an arc. by employing a compound magnetic field which is derived from a. magnet excited by a series winding as well as a shunt winding. As a result of this feature the arc column is maintained in its axial position both during the starting and restarting intervals as well as during the normal operation of the lamp.

A further feature relates to the combination of an arc discharge lamp having an el troma gnetic control device for the are column, the control device being provided with two differentially wound coils one coil being connected in shunt to the arc column, and the other coil being connected in series with thearc column. This arrangement is particularly useful in'maintaining the position of the arc column stable during the starting period of the lamp, and especially so during that part of the starting period where the convection currents in the hot gases and 0 vapors are establishing themselves. During this I period, if the shunt winding alone'were effective,

there might be over-correction of the arc position and a tendency of the arc column to approach the lower wall of the lamp. The addition of the series coil with its magnetomotive force opposing that of the main shunt coil reduces this tendency to over-correction. 4

A still further feature relates to an are discharge lamp arranged to.be operated with its longitudinal axis substantially horizontal, in conjunction with an electromagnetic arc control device mounted above the lamp and so arranged that the magnetic flux opposes the tendency of the arc colunm to bow towards the lamp walls.

Another feature relates to the novel organization, arrangement and relative location of parts which go to make up an improved high pressure vapor or gaseous arc lamp.

Other features and advantages not specifically enumerated .will be apparent after a consideration of the following detailed descriptions and the appended claims.

While the invention will be disclosed herein as applied to one form of gas or vapor arc lamp it will be understood that this is done merely for explanatory purposes and not by way of limitation to the particular lamp described. Furthermore only those parts of a high pressure gas or vapor arc lamp are shown which are necessary 40 to an understanding of the invention. Accordingly in the drawing, 1

Fig. 1 is a view, partly in vertic'al section, of a lamp and an arc control arrangement according to the invention.

Fig. 2 is a vertical'end view of the lamp and control means of Fig. 1 showing the relation between the magnetic fiux and the arc colunm.

Fig. 3 is a schematic view of Fig. 1 showing more clearly the relation between the main or resides in an arc through an ionizable medium at relatively high pressure. While the ionizable medium may be a metallic vapor it is preferably constituted of mercury vapor to which is added a small percent of an inert gas or gases such as neon, argon, etc., to facilitate starting. Thus suflicient mercury is introduced into the lamp so that when the lamp is in normal operation the pressure of the mercury vapor within the envelope may be of the order of from 0.5 to 1.5 atmospheres, although it will be understood that these figures are merely illustrative, and a greater or less quantity of mercury may be employed. The lamp may consist in general of an inner or main enclosing envelope I of a suitable transparent glass into the opposite ends of which are sealed the electrodes 2, 3 preferably of refractory material such as tungsten, molybdenum or the like. If desired, one or both of the electrodes may carry a quantity of electron emissive material such as an oxide or mixture of oxides of the alkaline earth metals. The main enclosing envelope i may be suitably mounted, as by resilient ring supports 4, 5, within an outer or heat conserving envelope 6 of suitable transparent material. Envelope 6 may be provided with any well-known form of contact base such for example as the threaded metal shell base 1 insulatingly carrying the usual metal contact button 8%. The lead-in wires for the electrodes 2 and 3 are connected to the shell and contact button respectively. If desired an auxiliary starting electrode ill in the form of a wire coil or wire mesh may be provided around the envelope l adjacent one end thereof. For a more detailed description of a lamp of this character referencemay be had to application Serial No. 758,405, filed December 20th, 1934.

Preferably the above-described lamp is arranged to be operated in a horizontal or at least a non-vertical plane, and unless means are provided for controllingthe are, the latter will bow upwardly as indicated by the dotted lines and may eventually strike the wall of the envelope I. In accordance with the present invention the lamp is provided with an arc control device in the form of an electromagnet which is preferably provided with two separate windings differentially wound one winding being connected in shunt to the arc column and the other winding being connected in series with the arc column. During the starting interval the voltage drop across the lamp is relatively low while the current drawn by the lamp is relatively high. During this starting period the pressure range of the metallic vapor filling may vary from 0.3 to 1.0 atmospheres and the arc column tends to bow up-' wardly toward the upper wall of the lamp probably because the convection currents within the hot vapors and gases are in the process of establishing themselves. On the other hand, when the lamp reaches its operating state the voltage dropacross the arc is relatively high and the arc current is relatively low. Ihave taken advantage of these phenomena to provide means to control the axial position of the are not only during the time the lamp is in normal operation but especially during the starting and restarting periods. For this purpose there is mounted in predetermined spaced relation to the lamp an electromagnet comprising a magneticcore H, preferably laminated, and a pair of magnetizing windings l2, l3. The core is preferably of about the same length as the lamp and of about the same Width as the diameter of the lamp and the magnetizing coils'are preferably wound differentially as indicated in Figs. 3 and 4. Preferably also, the magnet is mounted above the lamp and if desired the magnet may be provided with supporting brackets I4, l5 by whichthe spacing between the lamp and magnet may be adjusted. As shown more clearly in Figs. 2 and 4, the magnet is so mounted that the resultant magnetic flux, passes through the lamp at substantially right angles to the length of the arc column. If the lamp is being operated from a source of direct voltage, then the magnet should be disposed in the manner indicated so that the current is flowing through the arc in the direction indicated by the conventional cross, that is into the plane of the paper while the magnetic flux is indicated in the conventional manner by the arrows. This same relation between the resultant magnetic fiux and the arc current should beutilized when the lamp is being operated from a source of alternating voltage, so that reversals of the voltage are substantially synchronous with reversals of the current through the arc.

The connectionsare preferably such that the winding i2 is connected in series with the arc column, while the winding I3 is connected in shunt with the arc column. I have found that with this arrangement it is possible to so design the windings with relation to the starting and operating conditions of the lamp that the resultant magnetic field of the magnet overcomes the tendency of the arc column to bow upwardly. The starting period is usually accompanied by a decided tendency of the arc column to bow upwardly toward the upper wall of the lamp and also by a greater arc current than that which exists during the normal operation of the lamp. Should the shunt winding alone be used the greater starting current woulditend to overcorrect the position of the arc column and therefore the series winding is employed so that by their conjoint differential action the tendency to overcorrection during the starting and restarting periods is avoided. During the starting condition the current is relatively high so that fewer ampere turns are needed in the series winding to prevent the tendency of the shunt winding to over-correct. When the lamp has reached its operating condition the arc current drops while the voltage across the arc rises, and the resultant magnetic field of the shunt winding and the series winding maintain the arc in its central or substantially axial position.

As an example of one particular lamp that was found to produce the desired results, the length of the lamp was approximately 19 inches, and the diameter 2 inches. The lamp when cold had a vapor pressure of mercury filling of approximately -x10- atmospheres and the average starting current was 12 amperes with a voltage across the lamp supply conductors i6, I! of 20 volts. The control magnet was positioned approximately 3%" from axis of the lamp and the winding 12 was designed for 10 turns, while the winding it was designed for 1200 turns with .033 ampere at starting and .6 ampere normal. When .the lamp reached its normal operating condition the arc current was approximately 6 amperes and the pressure of the vapor filling was approximately 0.9 atmosphere. It will be understood that the invention is not necessarily limited to the provision of an 'arc control device for use with a horizontally disposed lamp, but

that the principle of the invention is capable of application to lamps operated in any position where the arc column is to be maintained in an axial or other predetermined position. Preferably the'lamp is operated with its longitudinal axis substantially horizontal and with the control magnet mounted above the lamp, because in this position the arc column is maintained with greater stability than when the magnet is mounted below the lamp. When the magnet is mounted below the lamp the arc is deflected by the resultant magnetic field in the direction of increasing field strength with the result that any momentary deflection of the arc column toward the magnet will be exaggerated. On the other hand, when the magnet is mounted above the lamp the column is deflected by the resultant magnetic field in the direction of decreasing field strength with greater stability in the arc position.

Various changes and modifications may be made herein without departing from the spirit and scopeof the invention.

What I claim is:

1. In combination, an electric arc lamp. of the high pressure vapor type and an electromagnet to control the position of the discharge therein, said electromagnet having differentially connected windings, the terminals of one of the windings being conductively and directly connected to the terminals of. the lamp.

2. In combination, a horizontal electric arcmagnet consisting of a laminated pile of several horizontally placed sheets of magnetic material. said core being of the same length and width as the discharge tube of the lamp.

3. In combination, an electric arc lamp of the high pressure vapor type and an electromagnet to control the position of the discharge therein, said electromagnet having differentially connected windings, the terminals of one of the 'windings being conductively and directly connected to the terminals of the lamp, the latter coil having more than 100 times as many turns as turns of the magnet winding being in planes,

parallel to said vertical plane, said winding consisting of two differentially connected coils one of said coils being connected in series with the arc, the other being connected directly across the arc terminals.

5. The combination of claim 1 in which the phase angle with respect to the lamp of the winding connected to the terminals of the lamp is substantially fixed solely by the electrical constants of the winding.

6. In combination, an electricarc lamp of the high pressure vapor type, and an electromagnet to control the position of the discharge therein, said electromagnet having a winding conductively and directly connected in shunt to the lamp, the phase angle of this shunt winding with respect to the lamp between determined solely by the electrical constants of said winding and of said lamp.

I LAURENCE BURNS. 

